
/*
 * -- SuperLU routine (version 2.0) --
 * Univ. of California Berkeley, Xerox Palo Alto Research Center,
 * and Lawrence Berkeley National Lab.
 * November 15, 1997
 *
 */
/*
 * File name:	dlangs.c
 * History:     Modified from lapack routine DLANGE
 */
#include <math.h>
#include "slu_ddefs.h"

double dlangs(char *norm, SuperMatrix *A)
{
    /*
        Purpose
        =======

        DLANGS returns the value of the one norm, or the Frobenius norm, or
        the infinity norm, or the element of largest absolute value of a
        real matrix A.

        Description
        ===========

        DLANGE returns the value

           DLANGE = ( max(abs(A(i,j))), NORM = 'M' or 'm'
                    (
                    ( norm1(A),         NORM = '1', 'O' or 'o'
                    (
                    ( normI(A),         NORM = 'I' or 'i'
                    (
                    ( normF(A),         NORM = 'F', 'f', 'E' or 'e'

        where  norm1  denotes the  one norm of a matrix (maximum column sum),
        normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
        normF  denotes the  Frobenius norm of a matrix (square root of sum of
        squares).  Note that  max(abs(A(i,j)))  is not a  matrix norm.

        Arguments
        =========

        NORM    (input) CHARACTER*1
                Specifies the value to be returned in DLANGE as described above.
        A       (input) SuperMatrix*
                The M by N sparse matrix A.

       =====================================================================
    */

    /* Local variables */
    NCformat *Astore;
    double   *Aval;
    int      i, j, irow;
    double   value, sum;
    double   *rwork;

    Astore = A->Store;
    Aval   = Astore->nzval;

    if ( SUPERLU_MIN(A->nrow, A->ncol) == 0) {
        value = 0.;

    } else if (lsame_(norm, "M")) {
        /* Find max(abs(A(i,j))). */
        value = 0.;
        for (j = 0; j < A->ncol; ++j)
            for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++)
                value = SUPERLU_MAX( value, fabs( Aval[i]) );

    } else if (lsame_(norm, "O") || *(unsigned char *)norm == '1') {
        /* Find norm1(A). */
        value = 0.;
        for (j = 0; j < A->ncol; ++j) {
            sum = 0.;
            for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++)
                sum += fabs(Aval[i]);
            value = SUPERLU_MAX(value,sum);
        }

    } else if (lsame_(norm, "I")) {
        /* Find normI(A). */
        if ( !(rwork = (double *) SUPERLU_MALLOC(A->nrow * sizeof(double))) )
            ABORT("SUPERLU_MALLOC fails for rwork.");
        for (i = 0; i < A->nrow; ++i) rwork[i] = 0.;
        for (j = 0; j < A->ncol; ++j)
            for (i = Astore->colptr[j]; i < Astore->colptr[j+1]; i++) {
                irow = Astore->rowind[i];
                rwork[irow] += fabs(Aval[i]);
            }
        value = 0.;
        for (i = 0; i < A->nrow; ++i)
            value = SUPERLU_MAX(value, rwork[i]);

        SUPERLU_FREE (rwork);

    } else if (lsame_(norm, "F") || lsame_(norm, "E")) {
        /* Find normF(A). */
        ABORT("Not implemented.");
    } else
        ABORT("Illegal norm specified.");

    return (value);

} /* dlangs */

